The present invention relates to a method for recording and analyzing event-related potentials (ERP), and more particularly to a method of measuring and determining P3 responses from a repeatedly presented stimulus or stimuli interspersed with non-significant stimuli and analyzing the measured ERP responses by means of a computer.
An electroencephalograph (EEG) is a device which measures and records brainwave activity by sensing spontaneous electrical potential of a person's scalp, cortex or cerebrum at various sites. Each EEG channel corresponds to a particular electrode combination attached to the patient. The sensed EEG potential at each channel is amplified by a differential amplifier, and the amplifier output signal is typically used to control movement of the recording pen of a polygraph. The EEG record is a long strip of polygraph paper containing a wave form for each EEG channel. The polygraph paper is driven at a pre-determined rate (e.g., 30 millimeters per second) and is graduated to represent predetermined time increments. A skilled neurologist must evaluate the EEG record to determine abnormalities in the EEG wave forms.
EEG signals exhibit different frequencies depending upon varying activity. The EEG signal frequencies are classified into four basic frequency bands, which are generally referred to as "Delta" (0-3.5 Hertz); "Theta" (4 to less than 8 Hertz); "Alpha" (8-13 Hertz); and "Beta" (greater than 13 Hertz). The neurologist determines the predominant frequency of a particular channel during a particular time period by measuring the period of the EEG signal wave form shown on the EEG record. This requires considerable training and is highly dependent upon the skill of the neurologist, since the EEG signal wave form typically includes multiple frequency components. EEG can be driven by specific extrinsic or endogenous events. For example, a regularly occurring stimulus will elicit a series of waves each time it is presented. The entire series is referred to as an event-related potential (ERP).
Besides the frequency of the EEG or ERP wave forms, the amplitude is often analyzed. Significance has been established when large amplitudes of brain waves occur at about 300 ms or more after the eliciting event. There is evidence to suggest that this P300 wave process is invoked when the updating, or "refreshing", of representations in working memory is required. Donchin, Psychophysiology, 18, 493-513 (1981); Fabiani, Karis, and Donchin, Psychophysiology, 22, 588-589 (1985); and others. Large P300's are elicited by rare or unexpected events, when they are relevant to the task the subject is performing. Such events may lead to restructuring or updating of working memory, and this activity is part of the ongoing process of maintaining accurate schemas of the environment. The updating process may lead to an "activation" of the representation, or to the "marking" of some attribute of the event that was crucial in determining the updating process. This restructuring of the representation of an event is assumed to facilitate the subsequent recall of the event, by providing valuable retrieval cues, so that the greater the restructuring that follows an individual event, the higher the probability of later recalling that event. If P300 amplitude represents the degree of restructuring in working memory, then P300 amplitude should also predict later recall. Fabriani, Karis and Donchin, Psychophysiology, Vol. 23, 298-308 (1986).
In view of the current knowledge of the frequency and amplitude of brain wave forms and with the advent of widespread use of the computer in behavioral neuroscience, the analysis of data has become easier.
Oftentimes, it is desirable to have an objective method of determining whether or not a person has seen or otherwise has knowledge of a particular item, such as a weapon, a crime scene configuration, a secret document, a stolen object, or another person's face. Such knowledge is what is taught by prior art procedures and devices used in "guilty knowledge" tests, a sub-category of procedures used in physiological detection of deception ("lie detection"). The present invention is directed to a reliable, valid easy-to-use and accurate procedure for determining guilty or other knowledge on the part of an individual whose simple verbal report may be unreliable for various reasons.
If a discreet stimulus--a sound, a light flash, a tap --is presented to a human, his electroencephalogram shows a series of time-locked responses called event related potentials (ERP). It was shown in the 1960's that if a subject is presented with a series of stimuli of two types, e.g., a high tone and a low tone, and if either of those tones is presented in 20 of 100 trials (with the remaining 80 trials containing the other tone), the rare stimulus will evoke a large ERP referred to as "P3" or previously described P300 brain wave. In this so-called "odd-ball" paradigm, it is known that P3 amplitude varies with rarity. Sutton, S. et al., Science, 150, 1187-1188, (1965).
In the 1970's and thereafter, other workers reported that P3 is evoked by words (or pictures) previously seen by a subject when presented in a word (or picture) series which also includes novel words (or pictures) which fail to evoke P3. Karis, D. et al., Cognitive Psychology, 16, 177-216; Neville, H. et al., Proc. Nat. Ac. Sci. U.S.A., 79, 2121-2123, (1982).
The present invention relates to a novel method which utilizes both the aforementioned effects so that one can tell by ERP inspection alone, which of the presented stimuli has previously been seen by the subject. The invention further relates to an apparatus which provides means for a repeated presentation of the significant stimulus and means for analyzing the ERP responses to determine significant P3 responses.
Sutton supra used P3 responses in an "odd-ball" procedure with simple auditory stimuli, e.g. high tones and low tones, that were presented singly to subjects and whatever tone was presented less often evoked a P3 response. Pritchard, et al., Psychophysiology, Vol. 23, No. 2, 166-172 (1986) utilizes the "odd-ball" paradigm in which the stimuli is a simple visual flash differing in brightness. R. Johnson, Jr. Annuals of the N.Y. Acad. of Sci., Vol. 425, pp. 223-230 (1984), like Pritchard, discuss studies utilizing P3 responses relating to memory updating processes, expectancy processes, surprise, and so forth. None of the prior art articles disclose the odd-ball procedure with repeated, meaningful word stimuli in the context to be utilized to detect guilty knowledge or other recognition processes. Fabiani, et al. Psychophysiology, Vol. 23, pp. 298-308 (1986) and Neville, et al. supra utilize verbal, meaningful stimuli in a variant kind of "odd-ball" bearing on recognition memory, however, but differ greatly from the present invention by two aspects: (1) these studies were not and could not be configured as field-relevant deception detection paradigms, because (2) both novel and previously seen words (or pictures) in these studies were never repeated within the EEG run. The average ERP to previously seen words [or pictures) was an average of responses to a series of all different words (or pictures); the average ERP to novel words (or pictures) was likewise an average of responses to all different novel words (or pictures). This kind of paradigm is likely to be specifically unsuited to real criminal-type investigations since it is usually a single item (the murder weapon, the stolen item, the classified document), which is involved in a real crime. The Fabiani and Neville reports are directed at and tailored to scientific elucidation of memory processes. In these studies, the repetition of words is avoided for fear of engaging habituation processes which would tend to reduce P3 effects.
In the present invention, the "odd-ball" item is "odd-ball" by virtue of its familiarity (e.g., as guilty knowledge). The stimuli are all meaningful words, and they are presented in the simplest possible, basic "odd-ball" design.
There are other studies in the literature which do not use quasi verbal stimuli which are repeatedly presented. A review of the literature reveals that these studies are not using "odd-ball" paradigms, and are, in fact, studying memory processes with extremely complicated procedures tailored to these purposes: For example, Gomer et al., Physio. Psych., Vol. 4 (1) pp. 61-65 (1976), (1976), Ford, et al., Elect. Clin. Neuroph., 47:450-459 (1979), Kramer et al. Psychophysiology, Vol. 23 No. 1, 33-47 (1986) and Adam and Collins, Elec. Clin. Neuroph. 44:147-156 (1978). All use "go-no go" or pattern matching paradigms. A set of letters or numbers is memorized and then the subject is given a trial series in which he decides whether ("go") or not ("no go") a memorized target stimulus is presented. There are typically other differences between these procedures and the present invention: The present invention requires but one series of trials; others use several sets. The present invention requires no feed-back whereas the prior art methods do. The prior art methods use warning tones whereas the present invention does not. It is notable that typically, the prior art reports P3 responses to both target and non-target stimuli. Although target effects are often reported to be bigger, unambiguous use of P3 responses in field investigations of deception requires the kind of virtually all-or-none results that are seen in the present invention. Further, the prior art studies use simple stimuli, digits or letters, rather than meaningful words. The intent of the prior art methods was the elucidation of memory retrieval processes and are more often interested in P3 latency than in amplitude.
Instruments have been used to determine psychological stress, for example, the apparatus described in U.S. Pat. No. 2,944,542relates to a blood pressure measuring device that indicates variations in the velocity of pulse waves, thereby indicating a change in emotional state. U.S. Pat. No. 3,971,034 describes a method and apparatus for identifying psychological stress by converting oral impulses into electrical signals and recording, observing and analyzing those signals. U.S. Pat. No. 3,893,450 relates to a method and apparatus for examining brain wave form by providing stimuli such as light and determining the characteristic of a mathematically determinal point in the brain wave forms of the subject. U.S. Pat. No. 4,188,956 relates to a method of acquiring compressing and analyzing neurometric test data by means of a digital computer base system. U.S. Pat. No. 4,579,125 relates to a method for processing analog EEG signals to provide an indication of cerebral activity. None of the teachings of these references however, have been used for the combination of a method to determine P3 responses from a repeatedly presented stimulus interspersed with non-significant stimuli to obtain results directed towards lie detection and control question testing.